1. Field of the Invention
The present invention relates to a clamping device for an injection blow molding machine capable of injecting a preform and blowing or stretch blow molding a hollow molded article such as a bottle in the same machine.
2. Detailed Description of the Prior Art
In the case of a vertical clamping device for a conventional injection blow molding machine, a clamping ram installing a booster ram is connected to a movable plate to which an injection core is set, so that the movable plate can be vertically moved and clamped by the claming ram. (Refer to the U.S. Pat. No. 5,062,787.)
In the case of the above prior art, the booster ram is set in the hollow clamping ram positioned below the upper portion of a clamping cylinder and, by the booster ram, the clamping ram is contracted in the clamping cylinder to move upward the movable plate connected to the lower end of the clamping ram. A clamping board and a plurality of injection cores fixed to the clamping board downward are mounted on the under face of the movable plate.
In the case of the above prior art, even if the movable plate is guided and held by the tie bars, all of the load of the movable plate is applied to the clamping ram, so the booster ram moves upward along the clamping ram against the load. Therefore, burden of the booster ram increases and, for reducing the burden, it opens a mold together with an upper base plate for a while. Consequently, the function of the booster ram normally used for opening and closing is not sufficiently shown. Moreover, because the booster ram supplies pressurized oil to the clamping ram through a thin flow passage bored in the ram, a problem occurs that oil-pressure resistance increases and it is difficult to open the mold at a high speed.